a fresh panther with a damaged engine from at grenade
Considering the panther needs to damaged below 75% to get that critical from an AT nade, my guess is that your two conscripts threw AT nades right out? Both hit with the second damaging the engine?
Also, with two conscript squads with the ATGs, if that panther is just shooting at the ATGs, use merge or recrew the ATGs with them. The panther is not that great at killing infantry.
Also don't expect your ATGs and support weapons to really maintain vet. They're likely going to be decrewed, which is what those conscripts are for.
And lastly, unsupported ATGs, especially a single one, are almost entirely useless. Always pull ATGs back and forward with your forces.